A significant body of prior art relating to IVT machines of the above type exists. Typical examples of these are described in the following publications: U.S. Pat. No. 4,878,883, GB2062142A, GB2135743A, U.S. Pat. Nos. 4,618,331, 3,956,944 and 5,984,814.
It will be seen from the specifications of U.S. Pat. Nos. 4,618,331 and 3,956,944 that these machines largely consist of radially positionable engagement devices that operate, either by means of sprocket teeth or frictionally, within fixed tracks which are spaced radially about the variable sprocket hub. Because of the limited number of engagement devices the flexible member track around them does not constitute a circular arc and their outputs are as a result, pulsed. Another problem with these prior art machines is the non-exact synchronisation of their engagement devices with the flexible member (chain) links where engagement is accomplished via spring loaded sprocket teeth or rotatable full sprockets operating in the fixed guides which make these devices only suitable for low speed applications, for example, on bicycles. In high speed and high torque applications the above prior art machines are not suitable.